DOI: https://doi.org/10.21894/jopr.2023.0054
PALM KERNEL MEAL ACTIVATED CARBON VIA GLASS WOOL-PYROLYSIS METHOD FOR
CEFTRIAXONE ADSORPTION
ACHMAD GUS FAHMI1; ZAENAL ABIDIN2*; CECEP KUSMANA3 and ERLIZA NOOR4 ABSTRACT
Antibiotic residues are a primary environmental concern because they are difficult to remove, including in wastewater treatment plants. A one-pot glass wool-pyrolysis method was developed and utilised to convert palm kernel meal into activated carbon from palm kernel meal (AC-PKM) over process temperatures 750°C for 5 hr as an adsorbent for antibiotic residues. Physicochemical properties, semi-quantitative specific surface area, surface functional group profiles, and scanning electron microscopy (SEM) were evaluated.
The physicochemical properties of AC-PKM meet the standards set by SNI 06-3730-1995 with a semi- quantitative specific surface area of 751 m2/g. Fourier transform infrared (FTIR) analysis shows that the active functional groups are scattered on the surface of AC-PKM. The maximum adsorption capacity is 82.64 mg/g adsorbent and can be explained by the Langmuir isotherm and pseudo-second-order type I kinetic model. The thermodynamic investigation showed that the adsorption process is a spontaneous endothermic reaction. The AC-PKM can remove 26% ceftriaxone (as a model residue antibiotic) for 2 hr of contact at a neutral pH at room temperature. The results show great promise of the one-pot glass wool-pyrolysis method to produce desirable activated carbon for removing ceftriaxone (CFT) application and an alternative treatment for the reuse of palm kernel meal waste.
Keywords: adsorption, ceftriaxone, glass wool, palm kernel meal, pyrolysis.
Received: 21 July 2022; Accepted: 14 August 2023; Published online: 26 October 2023.
1 Graduate School of Natural Resources and Environmental Management Science, IPB University,
16127 Bogor, Indonesia.
2 Department of Chemistry,Faculty of Mathematics and Natural Science, IPB University,
16680 Bogor, Indonesia.
3 Department of Silviculture, Faculty of Forest and Environment, IPB University,
16680 Bogor, Indonesia.
4 Department of Agro-Industrial Engineering, Faculty of Agriculture Engineering, IPB University, 16680 Bogor, Indonesia.
* Corresponding author e-mail: [email protected]
INTRODUCTION
Antibiotics are drugs used to treat bacterial infections. There is no doubt about the benefits of using antibiotics. However, if used excessively or not according to indications, it will lead to strains of bacteria resistant to antibiotics. Repeated and
irrational use of the same antibiotic can increase microbial resistance to that antibiotic (Olesen et al., 2018). Its increasing use in COVID-19 pandemic and antimicrobial resistance is a severe threat to public health that is experienced globally (Browne et al., 2021). Previous studies have explained that excessive use of antibiotics can lead to other diseases, such as diabetes mellitus (Mensah and Ansah, 2016) and cancer (Prajwal et al., 2017). The results of research conducted by Widayati et al. (2011) showed that antibiotic abuse does not only occur in health facilities but also in the community. Antibiotics are also used in livestock and fisheries, so antibiotic residues are considered persistent micropollutants in the aquatic environment.
Among various antibiotics, ceftriaxone (CFT) is the most common group in production and use in Indonesia because it has antimicrobial activity against various bacterial pathogens (Ayele et al., 2018). However, the CFT residue will enter the hospital wastewater treatment plant, which
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harms the aquatic environment and can hinder the progress of water treatment processes that use microbes. In addition, irrational use can lead to increased resistance to microorganisms and become a significant public health crisis (Al-Riyami et al., 2018). Therefore, efforts are needed to remove CFT residues from water so they are not harmful to the environment.
In recent years, various techniques have been investigated for the removal of CFTs from wastewater, including photocatalytic treatment, oxidation degradation (Kordestani et al., 2020), ultrasonic wave degradation (Shi et al., 2020), adsorption (Mahmoud et al., 2020), bio-electrochemical degradation (Hassan et al., 2021) and biological treatment (Bozorginia et al., 2021). Among these techniques, adsorption has been considered one of the most prospective approaches in the future because of its attractive advantages for the application of drug waste management in wastewater (de Ilurdoz et al., 2022). Several alternative adsorbents to overcome this problem are kaolin, bentonite (Song et al., 2019), polymer resins (Rivas et al., 2020), metal-organic framework (MOF) (Zango et al., 2020) and activated carbon (Schultz et al., 2020).
Important factors that constrain the selection and use of adsorbents are raw material availability, adsorption effectiveness, manufacturing method and production price. The challenges for raw material availability are overcome by using alternative raw materials derived from waste or recycling. In contrast, adsorption effectiveness, manufacturing methods and production prices are overcome by modifying production methods to produce adsorbents that have large surface areas, are easy, simple, and do not require expensive costs in manufacturing. One of the most widely used adsorbents, activated carbon, is the best alternative that can be chosen. Activated carbon can be produced from waste and has sustainable and environmentally friendly properties (Sharma et al., 2020). This potential can be an opportunity for tropical countries such as Indonesia because it fulfils promising aspects for providing such activated carbon adsorbents. However, even poorly managed biomass can cause serious environmental problems.
As one of the most widely used adsorbents, activated carbon is also considered a reliable solution for CFT removal due to its good performance (Schultz et al., 2020). On the other hand, activated carbon from palm fibres have a good adsorption capacity (57.47 mg/g adsorbent) in removing antibiotic residues in water (Acelas et al., 2021). One of the palm oil wastes that can be converted into activated carbon is palm kernel meal (PKM). PKM is a solid by-product of palm kernel oil extraction.
Oil palm biomass waste from empty fruit bunches, core meat, shells, and a mixture of them, has been
widely used as activated carbon as an adsorbent of organic compounds (Ukanwa et al., 2020).
Rugayah et al. (2014) used steam activation at high temperatures to make activated carbon from palm shells. This condition produces activated carbon with an adsorption capacity of 80.7% or 8.83 mg/g compared to commercial activated carbon. However, the continuous high-temperature steam method causes the production cost to increase. According to Osman et al. (2016), the one-step physical activation method can reduce production costs. The single- step physical activation method has a surface area of 523 m2/g with an organic compound adsorption capacity of 13-38 mmol/g adsorbent (Fahmi et al., 2019). In addition, modification of glass wool in the process of making activated carbon has the benefit of increasing the percentage yield, reducing the amount of ash formed and providing activated carbon with surface functional groups maintained (Fahmi et al., 2022). However, applying activated carbon products from PKM with physical activation has not been widely used to remove antibiotic waste in water. Therefore, this study discusses the properties of AC-PKM by the one-pot glass wool pyrolysis method developed by Fahmi et al. (2019) and relevant factors for CFT removal in wastewater.
MATERIALS AND METHODS Materials
Granule PKM waste was collected at a palm oil plant in South Kalimantan, Indonesia. All the chemicals used were obtained from Sigma-Aldrich®, while the commercially activated carbon used as control (ACC) was purchased from a chemical store in Bogor. The antibiotics model used in all the experiments was CFT, a sodium salt. The structure of CFT is given in Figure 1.
Procedures
Sample preparation. Waste PKM was collected from the oil palm industry in South Kalimantan. To remove contaminants, the sample was washed with distilled water before drying in the oven for 24 hr at 105°C. The dried materials were cut into small pieces and ground to 100 mesh using fibre grinder (Model 4 Wiley Mill Machine, Thomas Scientific USA) at 5000-6000 rpm.
Synthesis of AC-PKM followed the modified method by Fahmi et al. (2019). 5 g of PKM powder was added in crucible porcelain-coated glass wool all around.
Then the porcelain crucible was heated at 750°C in a 47900 Thermocline furnace (Barnstead International, USA) for 5 hr. This process took 3 hr for carbonisation and 2 hr for physical activation with characteristics of activated carbon showed in Fahmi et al. (2022).
It was then cooled naturally to room temperature.
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Characterisation of activated carbon. Physico- chemical properties of AC-PKM, PKM, and ACC (as a control), such as pH, ash content and moisture content, were determined using standard methods for activated carbon. The pH value of activated carbon was determined according to American Standard Testing Method (ASTM) D3838-5 with 1 g of sample added to 100 mL of distilled water in a 250 mL beaker. After stirring continuously for 10 min, the activated carbon was filtered, and the filtrate solution acidity was determined using a pH meter.
The ash content of activated carbon was determined using the ASTM D2866-96 method. Moisture content was determined using the oven drying method as described in ASTM D2867-09. The specific surface area of activated carbon was calculated using semi- quantitative measurements (Okeola et al., 2012).
Surface functional groups were identified using Spectrum One Fourier transform infrared (FTIR) (Perkin-Elmer, USA). The morphology of AC-PKM was identified using a scanning electron microscope (JEOL JSM-IT 300, Tokyo, Japan). All chemical ingredients were obtained from Sigma-Aldrich®. Adsorption of CFT. CFT was employed as an antibiotic model because this drug is often used in hospital therapy. In evaluating the stability of CFT under acidic, alkaline, and heat conditions, the CFT solution (25 mg/L) was treated with acid at pH 1, alkaline at pH 13, and temperature at 40°C (313 K).
After being stored for 24 hr, the CFT solution was scanned using a Genesys 10S Ultraviolet visible (UV- Vis) spectrophotometer (Thermo Fischer Scientific, USA) at 200-400 nm wavelength to identify degradation or peak shift. Adsorption was carried out at pH neutral with the batch method for 24 hr at 25°C (298 K). A total of 10 mL of CFT solution with a concentration of 25-1000 mg/L was added to a tube containing AC-PKM sample as much as 0.01 g. After equilibrium, the adsorbent was separated under centrifugation, and the concentration of CFT on the
supernatant was measured using Genesys 10S UV- Vis spectrophotometer (Thermo Fischer Scientific, USA) at the maximum wavelength (274 nm). The adsorption capacity followed Equation (1):
qe = (Co-Ce) x V . (1) (m x 1000)
where qe is adsorption capacity (mg/g adsorbent), V is the volume of solution (mL), Co is the initial concentration of CFT (mg/L), Ce is the residual concentration of CFT (mg/L), and m is mass of adsorbent (g). Mathematical representation from the isotherm adsorption model was used to interpret CFT adsorption on the surface adsorbent, and its calculation refers to Langmuir and Freundlich isotherm model. The Langmuir isotherm model in its nonlinear form is expressed as in Equation (2) (Jasper et al., 2020).
qe = qmaxKLCe (2) 1 + KLCe
where, qe being adsorption capacity equilibrium of the adsorbent (mg/g adsorbent), Ce being the residual concentration (mg/L), qmax being adsorption maximum in Langmuir model (mg/g adsorbent), being Langmuir’s constant (L/mg) that represents affinity side active bond. The Freundlich isotherm model in nonlinear form is expressed as in Equation (3) (Jasper et al., 2020).
qe = Kf C n1_ (3) where, qe as adsorption capacity equilibrium (mg/g adsorbent), Ce is the residual concentration (mg/L), Kf (mg/g) (L/mg)(1/n), and 1/n is Freundlich constant denoting capacity adsorption and intensity adsorption. The process was solely based on Ce
Figure 1. Structure of sodium ceftriaxone.
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measurements. Following the statistical premise, Cassol et al. (2014) state that the method is more trustworthy and must be used to estimate the adsorption equilibrium parameters.
Kinetic and thermodynamic models. The method for analysing the adsorption kinetics was carried out with the same experiment as the adsorption measurement. The treatment was repeated by measuring the supernatant at different contact times (0-180 min). In addition, the effect of temperature on the adsorption process of CFT on AC-PKM was studied by varying the adsorption temperature at 30°C (303 K) until 40°C (313 K).
Removal of CFT. CFT removal was carried out at a CFT concentration of 250 mg/L as artificial wastes.
The quantity of CFT removal (%R) by AC-PKM was calculated as follows [Equation (4)].
%R = V (CO – Ce) × 100 (4) CO
where %R is percentage removal CFT (%), V is volume of solution (mL), Co is initial concentration of CFT (mg/L), and Ce is the residual concentration of CFT (mg/L).
RESULTS AND DISCUSSION Adsorbent Characteristics
Generally, activated carbon is synthesized at temperatures of 700°C-1000°C. In high-temperature condition, some of the carbon loses various functional groups on its surface and convert to ash. The presence of this surface functional group is significant because it plays a role in chemical processes for adsorption and catalysis. Xiao et al.
(2018) used a unique pyrolysis process to retain functional groups on the surface, and this method can increase specific surface area, porosity, and absorptivity. Thus, maintaining functional groups on the surface of activated carbon has benefits in utilising the activated carbon.
This study concentrated on the physical activation approach using glass wool as a material that can isolate heat and reduce oxygen during the activation process. Furthermore, adding glass wool to coat the reactor can cause the heat generated to be concentrated in the reactor core, making the pyrolysis process more efficient (Santhiarsa, 2021).
Our previous experiment used the glass wool pyrolysis method for coconut shell waste samples, effectively conducted at 750°C to produce activated carbon with large surface functional groups. This method can also increase biomass conversion into
activated carbon (Fahmi et al., 2019). In addition, the modification of glass wool in the process of making activated carbon has the benefit of increasing the percentage yield, reducing the amount of ash formed, and providing activated carbon with surface functional groups maintained (Fahmi et al., 2022).
Therefore, in this study, we used the similar method with different biomass effluents to apply ceftriaxone removal in hospital wastewater.
The physicochemical properties of the activated carbon are presented in Table 1. Based on the measurement results, it is shown that the pH values of AC-PKM and ACC were found to be in proximity of neutral pH, namely 6.80 and 6.98, respectively.
Generally, the acceptable pH range is 6.00-8.00 for applications in wastewater treatment (Ashtaputrey and Ashtaputrey, 2016). The presence of surface- active functional groups can affect the surface charge of the adsorbent (variable charge), which will affect the adsorption ability. Therefore, the pH value is crucial for adsorbents with surface-active functional groups to achieve the most excellent application performance.
TABLE 1 . PHYSICOCHEMICAL PROPERTIES OF AC-PKM COMPARED WITH COMMERCIAL ACTIVATED CARBON
(ACC) AND BIOMASS (PKM)
Parameter AC-PKM ACC PKM
pH 6.80 ± 0.2 6.98 ± 0.2 -
Ash content (%) 5.10 ± 1.0 3.10 ± 1.0 5.15 ± 1.0 Moisture content (%) 4.94 ± 1.0 3.94 ± 1.0 14.94 ± 1.0 Specific surface area
(m2/g) 751 ± 10 783 ± 10 407 ± 10
Another physicochemical property is ash content. Based on the measurement, the ash content of AC-PKM and PKM had the same values, which were 5.10% and 5.15%, respectively, while ACC has a lower ash content value of 3.10%. Ash content can affect the activated carbon quality, with the maximum in activated carbon being 15.00% (SNI 06-3730-1995). High ash content can reduce the absorption and specific surface area (De Gisi et al., 2016). In addition, the selection of biomass raw materials also affects the ash content in activated carbon. Low ash-content biomass has the potential as an excellent raw material for the manufacture of activated carbon (Feng et al., 2020).
Furthermore, AC-PKM has a relatively low water moisture of 4.94%, with the accepted standard value for activated carbon samples of 3.00%-6.00%
(Gumus and Okpeku, 2015). In addition, the high water moisture in activated carbon will dilute the adsorbent concentration, thus requiring more weight of the adsorbent to maintain the same adsorption capacity. Furthermore, the water moisture decreases with the carbonisation temperature due to the
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smaller pores of the activated carbon. The high water moisture is usually caused by the concentration of activator in chemical activation (Maulina et al., 2020). Ultimately, this phenomenon will increase the hygroscopic properties of absorbing water from the air (Tani et al., 2014). Hence, the selection of activator compounds and activation methods have an essential role in influencing the characteristics of the water moisture in activated carbon.
Based on the written reports, the value of Xm was used to calculate the specific surface area of monolayer coverage (Okeola et al., 2012). The specific surface area of AC-PKM is 751 m2/g, slightly lower than that of ACC (783 m2/g). According to Hu and Gao (2018), a high surface area can increase the adsorbability so that it will affect the adsorption capacity of the adsorbent. In addition, another factor that affects the adsorption ability is the surface interaction of the adsorbent with the adsorbate, which is predicted through the adsorption isotherm model (Wu et al., 2020). Activated carbon has various pores, so further analysis is needed to show the presence of macropores, mesopores and micropores.
In addition, the adsorption performance of carbon-based adsorbents is highly dependent on the surface-active functional groups (Kharrazi et al., 2021). In this study, the various surface-active functional groups of AC-PKM, ACC, and PKM was identified using FTIR spectroscopy (Figure 2). The AC-PKM and PKM show a broad spectrum around 3445 cm-1 and 600 cm-1 with different intensities and shapes of the spectra. Meanwhile, the ACC found that the peak loss was at the wavenumber at 3445 cm-1, which is a stretch of O-H and 600 cm-1 from the =C-H bending of the aromatic ring. Another FTIR spectrum of ACC differed in intensity from the spectrum of AC-PKM and PKM. The C=O (1500-
1650 cm-1) and C-O (1000-1050 cm-1) stretches had low intensity in the spectrum of ACC, and the CC (2366 cm-1) stretch band was weak. However, the similarity of the spectrum of AC-PKM with the initial biomass (PKM) is identical, which indicates that there are similar functional groups. Thus, the glass wool-pyrolysis method can maintain the intensity of the spectrum compared to ACC, where the spectrum is significantly weakened or even disappears.
Based on the spectrum data analysed for each adsorbent produced, it can be seen that AC-PKM has a peak in the FTIR spectrum in the form of some active surface groups. Therefore, the morphology of AC-PKM was confirmed using Scanning Electron Microscope (SEM). The identification results using SEM showed that on the surface of the AC-PKM pore, there was an unshaped bulk solid. In addition, these unshaped bulk solids can also reduce the pore size but provide interaction with the adsorbate adsorbed. As for ACC, there are no such shapeless bulk solids, which corroborates the statement of the presence of functional groups on the AC-PKM pore surface (Figure 3).
CFT stability experiments showed that CFT has high stability in heat treatment because there was no significant change (24 hr, 40°C) (Figure 4). Roca et al.
(2011) suggest that β-lactam antibiotics such as CFT will undergo thermal decomposition gradually at a temperature of 60°C-100°C following pseudo-first- order kinetics. Meanwhile, at room temperature (23 ± 2°C), structurally, CFT is very stable for up to 4 days (De Diego et al., 2010). However, in the acid-base treatment, there were (hyperchromic and bathochromic) shifts in the peak of the CFT, which indicated that it was unstable (Figure 4).
This condition is caused by the side reactions, such as hydrolysis, and side functional groups, such as
Figure 2. The infrared spectrum of ACC (green line), AC-PKM (red line) and PKM (black line).
Transmittance
Wavenumber (cm-1)
4 000 3 000 2 000 1 000
3 738
3 841 3 746
3 445
3 840 3 739
3 444
2 366
1 6421 425 1 042
600 2 367
1 6381 419 1 050
600 2 358 1 940 1 544 1 052
3 500 2 500 1 500 500
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amines and carboxyls, that affect the structural changes of CFT (Alekseev, 2010). Based on these results, adsorption measurements were carried out under neutral conditions according to the pH of the activated carbon and CFT.
CFT Adsorption
Sorption processes are well described by isotherms whose purpose is to help elucidate the interaction between sorbate and sorbent. They also provide information on the affinity of the sorbent for the sorbate. In this study, the Langmuir and Freundlich isotherm models were applied to observe the sorption of CFT onto the AC-PKM. All three adsorbents (ACC, AC-PKM and PKM) followed the Langmuir adsorption isotherm, consistent with the statistical premise with non-linear evaluation (Figure 5).
The isotherm models shown in Table 2 follow the Langmuir model for all three adsorbent types ACC, AC-PKM, and PKM. The linearity (R2) of the Langmuir adsorption isotherm model for ACC, AC-PKM, and PKM significantly differed from the
linearity (R2) of the Freundlich adsorption isotherm model. According to Cassol et al. (2014), this method is more reliable and should be used to determine adsorption equilibrium parameters. This isotherm model is routinely used to explore the adsorption characteristics of an adsorbent (Karri et al., 2017).
As for the two adsorption isotherm models, they have differences from the adsorption mechanism that occurs with various assumptions in each model. The Freundlich isotherm model predicts sites that do not interact with heterogeneous surfaces and exponential adsorption. In contrast, the Langmuir model predicts sites that interact with the heterogeneous surface and exponential adsorption.
Figure 3. Scanning electron microscope photograph of (a) AC-PKM, and (b) ACC.
Figure 4. UV spectrum of CFT in 200-400 nm with various treatments (acid, base and heat).
TABLE 2. LANGMUIR AND FREUNDLICH ADSORPTION ISOTHERM MODEL CONSTANTS
Adsorbent Langmuir Freundlich
qm b R2 Kf n R2
PKM 24.86 0.033 0.9891 20.19 44.05 0.1572 AC-PKM 82.64 0.037 0.9982 14.56 3.71 0.9162 ACC 153.85 0.029 0.9988 16.64 2.75 0.9091
Transmittance
Blank Acid treatment Base treatment Heat treatment
Wavelength (nm) 0.00200
1.00 2.00 3.00 4.00
0.50 1.50 2.50 3.50
300
250 350 400
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Figure 5. Nonlinear the Langmuir isotherm model fittings for CFT adsorption onto ACC, AC-PKM and PKM at room temperature.
The maximum adsorption capacity of each sample was determined by calculating the Langmuir adsorption isotherm (Figure 5). The maximum adsorption capacity value of PKM is 24.86 mg/g adsorbent was the lowest when compared to AC- PKM (82.64 mg/g adsorbent), and ACC (153.85 mg/g adsorbent). The activated carbon adsorption mechanism generally utilises wide pores or follows the Freundlich adsorption isotherm model (Ayawei et al., 2017). However, the presence of surface functional groups can affect the adsorption capacity. CFT adsorption in water was carried out at neutral pH, so the anionic CFTs dominated.
However, the negatively charged surface of AC- PKM electrostatically repels the incoming CFT anions and affects their absorption. Furthermore, competition of hydroxyl (-OH) functional groups for the active binding site on AC-PKM with CFT anions may contribute to the markedly perceived decrease in adsorption rates (Saied et al., 2022). Therefore, the adsorption capacity will decrease as the surface functional groups increase. The maximum monolayer adsorption capacity (qmax) was 82.64 mg/g adsorbent, comparable to values reported for CFT adsorption with several adsorbents (Table 3).
The dependence of pH on CFT stability (Figure 4) implies that the removal of CFTs under neutral conditions cannot be ascribed to electrostatic interactions. This is because the CFT used as a drug is a sodium salt compound easily soluble in water with a pH of around 6.7 (Khan et al., 2017).
In addition, the crystal structure of CFT has many OH---O hydrogen bonds involving water molecules and an ionised portion of the anion (Gonzalez et al., 2020), so it will produce a high electrostatic repulsion force with the surface-active group of
activated carbon, which is also negatively charged.
The electrostatic repulsion between AC-PKM and CFT can reduce the adsorption capacity of AC-PKM compared to commercial activated carbon (ACC).
The interactions that may form so AC-PKM can adsorb CFT are non-electrostatic interactions such as H-bonds, -π interactions, n-π electron donor-acceptor interactions, and hydrophobic- hydrophobic interactions (Saied et al., 2022).
Although there is a possible interaction between CFTs with π-π bonds in the activated carbon pores (Figure 6). Hydrogen bonds occur between the hydroxyl functional groups on the activated carbon surface and S, N, and O atoms in the CFT structure (C-OH---S, C-OH---N, and C-OH---O). Gonzales et al. (2020) report that hydroxyl molecules act as donors for ionised carboxylates and carbonyls. In addition, there are also intramolecular hydrogen
TABLE 3. COMPARISON OF MAXIMUM ADSORPTION CAPACITY OF CFT USING SAVERAL ADSORBENTS
Adsorbent qmax
(mg/g
adsorbent) References Activated carbon-Fe2O3 28.930 Badi et al.
(2018)
ZVI/SrFe12O19 8.084 Amiri et al.
(2020) NBent-NTiO2-Chit
nanocomposite 90.910 Mahmoud et
al. (2020) Bi2WO6/g-C3N4 photocatalyst 3.400 Zhao et al.
(2018)
ACC 153.850 Present study
AC-PKM 82.640 Present study
Ce (mg/L)
Langmuir Isotherm Adsorption
ACC
ACC non-Linear AC-PKM
AC-PKM non-Linear PKM
PKM non-Linear qe (mg/g)
0 200 400 600 800 1000
160 140 120 100 80 60 40 20 0
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bonds C13-H48-C10 with the carbon of the ionised carboxyl group. Another interaction that may occur in this adsorption process is between the carbonyls found on the activated carbon surface and triazine (aromatic) in the CFT structure. The n-π electron donor-acceptor interaction occurs when the carbonyl donates a lone pair of electrons (n), and the triazine accepts electrons in its system structure. According to Biasutti et al. (1992), nitrogen-substituted benzene, such as triazine, is an acceptor in the n-π electron donor-acceptor interaction. Therefore, the adsorption mechanism can be illustrated in Figure 6.
Kinetics and Thermodynamics Model of CFT Adsorption
Experiments to obtain CFT removal percentage were carried out at room temperature and neutral pH using an artificial CFT waste (250 mg/L). Gradually, the concentration of CFT in the residual solution was measured to obtain a stable condition at several points (Figure 7). Based on the measurements, the results showed that PKM could absorb the lowest value of 8%. The AC-PKM conversion using the glass wool-pyrolysis method can increase the percentage of CFT removal is to 26%. However, this value is still lower when compared to ACC (32%).
This percentage value has been able to eliminate the content of CFT in hospital wastewater with a concentration of 1.25-29.15 g/mL (Shipingana et al., 2022).
Adsorption is also a multistep process involving the transfer of dissolved substances to the surface, followed by diffusion of internal pores. Thus, kinetics adsorption gives valuable information for the
design need of big-scale adsorption columns. There are two types of kinetic study models, i.e., pseudo- first-order model and pseudo-second-order model.
The pseudo-first-order assumes that the interaction surface controls the adsorption process. In contrast, pseudo-second-order assumes that intra-particle diffusion controls the adsorption rate. Lagergren first proposed this kinetic study model to describe the adsorption of pollutant liquid on the surface solid and differentiate it from the kinetic system based on concentration (Vafakhah et al., 2016). The experimental results of the kinetic parameters are given in Table 4 and Figure 8. The linear correlation coefficient of AC-PKM (R2) against the pseudo- second-order kinetic model type I (R2=0.9961) was higher than that of the other kinetic model.
In addition, the experimental adsorption capacity value on pseudo-second-order kinetics model type I (qexp=82.64 mg/g) was close to the calculated one (qcal=72.9927 mg/g), indicating this kinetic model is more suitable for describing the data. Therefore, the phenomenon of CFT adsorption with AC-PKM is chemisorption (Yu et al., 2020).
Thermodynamic analysis was also carried out to predict changes in free energy (G°), enthalpy (H°), and entropy (S°) (Bhandari and Gogate, 2018). The adsorption usually involves dropping Gibbs free energy (∆G), accompanied by decreased entropy (∆S), because the adsorbed molecule is bound to the side of the active surface. The loss of degrees of freedom of adsorbed molecules compared with the state before adsorption causes a drop in free energy (∆G) and entropy (∆S). At the same time, enthalpy (∆H) depends on temperature during adsorption.
Temperature plays a vital role in adsorption. Change
Figure 6. Proposed adsorption mechanism of ceftriaxone as a model antibiotics residue in this study to activated carbon from PKM.
Adsorption mechanism Hydrogen bond Donor π-π
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PALM KERNEL MEAL ACTIVATED CARBON VIA GLASS WOOL-PYROLYSIS METHOD FOR CEFTRIAXONE ADSORPTION
TABLE 4. ADSORPTION KINETICS CONSTANTS OF PSEUDO-FIRST-ORDER AND PSEUDO-SECOND-ORDER ADSORPTION
Pseudo 1st Type I Pseudo 2nd Type II Pseudo 2nd
R2 qcal K1 R2 qcal K2 R2 qcal K2
PKM 0.0094 0.3887 0.0005 0.9966 21.5054 0.0044 0.9823 25.9740 0.0019
AC-PKM 0.4074 1.1220 0.0044 0.9961 72.9927 0.0008 0.9956 80.6452 0.0005
ACC 0.4750 1.5545 0.0039 0.9947 87.7193 0.0009 0.9830 98.0392 0.0005
Type III Pseudo 2nd Type IV Pseudo 2nd Type V Pseudo 2nd
R2 qcal K1 R2 qcal K2 R2 qcal K2
PKM 0.9823 26.4738 0.0018 0.8447 24.5563 0.0023 0,4038 11,2867 0,0005
AC-PKM 0.9956 81.1957 0.0005 0.9348 79.6690 0.0005 0,3849 12,1359 0,0004
ACC 0.9830 99.5606 0.0005 0.8310 100.2432 0.0005 0,3582 33,3333 0,0001
Proofs corrections
Journal Journal Of Palm Oil Research
Article ID/title JOPR-2022-0099R5 entitled "Palm Kernel Meal Activated Carbon Via Glass Wool-Pyrolysis Method for Ceftriaxone Adsorption”
Reviewer Correction author
Please provide text/picture for table 4
Type Non-linear form Linear form Plot Parameters
Pseudo first-order 𝑞𝑞 = 𝑞𝑞!(1 − 𝑒𝑒𝑒𝑒𝑒𝑒"#!$) log(𝑞𝑞!− 𝑞𝑞) = log(𝑞𝑞!) − 𝐾𝐾%𝑡𝑡
2.303 log(𝑞𝑞!− 𝑞𝑞) vs. 𝑡𝑡 𝐾𝐾%= −2.303 x slope Type 1 pseudo second-order
𝑞𝑞 = 𝐾𝐾&𝑞𝑞!&𝑡𝑡 1 + 𝐾𝐾&𝑞𝑞!𝑡𝑡
𝑡𝑡 𝑞𝑞= 1
𝐾𝐾&𝑞𝑞!&+1
𝑞𝑞!𝑡𝑡 𝑡𝑡 𝑞𝑞: vs. 𝑡𝑡 𝑞𝑞!= 1 slope: , 𝐾𝐾&= slope&Aintercept
Type 2 pseudo second-order 1
𝑞𝑞= B 1 𝐾𝐾&𝑞𝑞!&C1
𝑡𝑡+1
𝑞𝑞! 1 𝑞𝑞: vs. 1 𝑡𝑡: 𝑞𝑞!= 1 intercept: , 𝐾𝐾&= intercept&Aslope
Type 3 pseudo second-order 1
𝑡𝑡=𝐾𝐾&𝑞𝑞!&
𝑞𝑞 −𝐾𝐾&𝑞𝑞!&
𝑞𝑞! 1 𝑡𝑡: vs.1 𝑞𝑞: 𝑞𝑞!= −slope intercept: , 𝐾𝐾&= intercept&Aslope
Type 4 pseudo second-order 𝑞𝑞
𝑡𝑡= 𝐾𝐾&𝑞𝑞!&−𝐾𝐾&𝑞𝑞!&𝑞𝑞 𝑞𝑞!
𝑞𝑞: vs. 𝑞𝑞 𝑡𝑡 𝑞𝑞!= −intercept slope: , 𝐾𝐾&= slope&Aintercept
Type 5 pseudo second-order 1
𝑞𝑞!− 𝑞𝑞=1
𝑞𝑞!+ 𝐾𝐾&𝑡𝑡 1:(𝑞𝑞!− 𝑞𝑞) vs. 𝑡𝑡 𝑞𝑞!= 1 intercept: , 𝐾𝐾&= slope
Please provide a correct number in table 5
8812.7 (eight thousand eight hundred twelve point seven) Proofs corrections
Journal Journal Of Palm Oil Research
Article ID/title JOPR-2022-0099R5 entitled "Palm Kernel Meal Activated Carbon Via Glass Wool-Pyrolysis Method for Ceftriaxone Adsorption”
Reviewer Correction author
Please provide text/picture for table 4
Type Non-linear form Linear form Plot Parameters
Pseudo first-order 𝑞𝑞 = 𝑞𝑞!(1 − 𝑒𝑒𝑒𝑒𝑒𝑒"#!$) log(𝑞𝑞!− 𝑞𝑞) = log(𝑞𝑞!) − 𝐾𝐾%𝑡𝑡
2.303 log(𝑞𝑞!− 𝑞𝑞) vs. 𝑡𝑡 𝐾𝐾%= −2.303 x slope Type 1 pseudo second-order
𝑞𝑞 = 𝐾𝐾&𝑞𝑞!&𝑡𝑡 1 + 𝐾𝐾&𝑞𝑞!𝑡𝑡
𝑡𝑡 𝑞𝑞= 1
𝐾𝐾&𝑞𝑞!&+1
𝑞𝑞!𝑡𝑡 𝑡𝑡 𝑞𝑞: vs. 𝑡𝑡 𝑞𝑞!= 1 slope: , 𝐾𝐾&= slope&Aintercept
Type 2 pseudo second-order 1
𝑞𝑞= B 1 𝐾𝐾&𝑞𝑞!&C1
𝑡𝑡+1
𝑞𝑞! 1 𝑞𝑞: vs. 1 𝑡𝑡: 𝑞𝑞!= 1 intercept: , 𝐾𝐾&= intercept&Aslope
Type 3 pseudo second-order 1
𝑡𝑡=𝐾𝐾&𝑞𝑞!&
𝑞𝑞 −𝐾𝐾&𝑞𝑞!&
𝑞𝑞! 1 𝑡𝑡: vs.1 𝑞𝑞: 𝑞𝑞!= −slope intercept: , 𝐾𝐾&= intercept&Aslope
Type 4 pseudo second-order 𝑞𝑞
𝑡𝑡= 𝐾𝐾&𝑞𝑞!&−𝐾𝐾&𝑞𝑞!&𝑞𝑞 𝑞𝑞!
𝑞𝑞: vs. 𝑞𝑞 𝑡𝑡 𝑞𝑞!= −intercept slope: , 𝐾𝐾&= slope&Aintercept
Type 5 pseudo second-order 1
𝑞𝑞!− 𝑞𝑞=1
𝑞𝑞!+ 𝐾𝐾&𝑡𝑡 1:(𝑞𝑞!− 𝑞𝑞) vs. 𝑡𝑡 𝑞𝑞!= 1 intercept: , 𝐾𝐾&= slope
Please provide a correct number in table 5
8812.7 (eight thousand eight hundred twelve point seven)
in Gibbs free energy (ΔG) during the adsorption process could be calculated from its connection with thermodynamics based on Equation (5):
∆Gº = ∆Hº – T∆Sº (5) where G° is the change energy free standard (J/mol), H° is the heat adsorption standard (J/
mol), S° is the change in entropy during adsorption (J/mol K) and T is the temperature (K). The Van’t Hoff Equation (6) shows a relationship between the equilibrium constant and the free energy change.
∆Gº = – RT In Kº (6) Where R is an ideal gas constant of 8.314 (J/mol K) and K is an equilibrium constant. The
equilibrium constant was calculated from the ratio of equilibrium adsorbate concentration still in solution, Ce (mg/L), to the quantity of adsorbate adsorbed per gram of adsorbent at equilibrium, qe (mg/g). The following is how the equation for K is represented mathematically.
K = qe º (7)
Ce
In calculating the free energy change, equilibrium constant values were employed. The adsorption is usually confirmed to be spontaneous when the free energy change is negative. In order to derive the model parameters, Equation (5) was converted into a straight-line equation and plotted as G°/T vs. 1/ T.
Figure 7. Adsorption capacity of CFT removal (mg/g adsorbent) with the effect of contact time on ACC, AC-PKM and PKM biomass.
Type Non-linear form Linear form Plot Parameters
0 50 100 150 200
160 140 120 100 80 60 40 20 0
Contact time (min)
PKMACC AC-PKM
Adsorption capacity (mg/g)
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Figure 8. Pseudo-first-order and pseudo-second-order adsorption kinetics type I, II, III, IV, V plot of CFT removal on ACC, AC-PKM and PKM biomass.
Enthalpy and entropy values for adsorption were calculated using slope and intercept values. Table 5 includes the information obtained for G, H, and S.
The change in free energy (∆G°), enthalpy (∆H°) and entropy (∆S°) were all predicted using thermodynamic analysis. The data for G°, H°, and S° are shown in Table 5 and Figure 9. The adsorption process is endothermic with a positive adsorption enthalpy value. On the other hand, the entropy was positive, associated with an increase in the system’s randomness during adsorption. This thermodynamic parameter also shows that an increase in adsorption
capacity will be obtained with an increase in temperature. However, it should be noted that at temperatures above 60°C (353 K), β-lactam antibiotics such as CFTs can degrade rapidly (Roca et al., 2011).
CFT is an antibiotic widely used for surgical prophylaxis, pneumonia, respiratory infections and sepsis. The WHO (2014) recommended maximum daily dose of CFT is 2 g for adults (Anatomical Therapeutic Chemical/ATC J01DD04). Improper target use can increase the potential for CFT contamination in the waters. When the length of time the pollutant acts is examined, pollution
PKM AC-PKM ACC
PKM AC-PKM ACC
PKM AC-PKM ACC
PKMAC-PKM ACC
PKM AC-PKM ACC
PKM AC-PKM ACC 0
0
0 20 40 60 80 100
0 0 50
0.05 0.05
50 100
0.1 0.1
100 150
0.2 0.2
0.15 0.15
150 200
0.25 0.25
200 2.5
2.0 1.5 1.0 0.5 0.0
109 87 65 4 32 1 0
0.3 0.2 0.2 0.1 0.1 0.0
4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
0.2 0.2 0.1 0.1 0.0 -0.1 -0.1 -0.2 -0.2 0.3 0.2 0.2 0.1 0.1 0.0 t (min)
1/t
qt t
1/qt t (min) Pseudo 1st
Type II Pseudo 2nd
Type IV Pseudo 2nd
Type 1 Pseudo 2nd
Type III Pseudo 2nd
Type V Pseudo 2nd
Log (qe-qt) t/qt
1/qtqt/t 1/(qe-qt)1/t
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might be permanent, systematic, periodic, or accidental. The repercussions of water pollution have an impact on both the environment and human health (Gavrilescu, 2021). For this reason, reducing the risk of antibiotic residues from waste in hospitals is necessary. In this paper, adsorbent regeneration is not carried out because it is less economical and efficient. Thus, after adsorption, the adsorbent will be used as an alternative fuel.
Further research is needed to investigate the release of carbon dioxides and other gases produced, thereby avoiding more harmful side pollutants.
Indonesia is the world’s largest palm oil producer and produces PKM waste of 6 million tonnes per year. In addition, PKM waste is generally found in palm oil processing plants, making it easier to process it into activated carbon at a lower production price. Therefore, activated carbon based on PKM waste has great potential as an adsorbent that can be used as an alternative material in reducing antibiotic residues in water.
CONCLUSION
Modifying the glass wool-pyrolysis method at 750°C for 5 hr was developed to synthesize AC-PKM from palm kernel meal as an adsorbent for antibiotic residues. This method can maintain the surface-active functional groups on AC-PKM with a large specific surface area.
The adsorption isotherm model for AC-PKM follows the Langmuir isotherm model at room temperature. The adsorption process is endothermic and spontaneous. Kinetics studies showed that CFT adsorption on AC-PKM followed a pseudo-second-order kinetic model. AC-PKM adsorbent can remove CFT levels greater than PKM, which is 26%. Although the percentage removal of AC-PKM is still lower than that of ACC. AC-PKM has potential in removing CFT and is an alternative treatment for reuse PKM biomass waste.
TABLE 5. THERMODYNAMIC MODEL FROM SAMPLE Sample Temperature (K) ΔG
(J/mol) ∆H
(J/mol) ∆S
(J/mol K)
PKM 298 289.73
8812.7 17 251
303 268.30
313 176.65
AC-PKM 298 -1 455.92
19 496.0 55 346
303 -1 435.98
313 -1 344.59
ACC 298 -2 071.71
25 768.0 78 193
303 -1 763.25
313 -1 603.37
Figure 9. Van’t Hoff Plot of CFT removal on ACC, AC-PKM and PKM biomass.
PKM AC-PKM ACC 14
12 10 8 6 4 2 0
1/T
0.00315 0.0032 0.00325 0.0033 0.00335 0.0034
Van’t Hoff Plot
∆G/T
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ACKNOWLEDGEMENT
This work was funded by PMDSU Scholarship, the Ministry of Educational and Culture of Republic Indonesia (Grant Number 4160/IT3.L1/PN/2020).
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